Sensitometer



Au 22, 1939. J, c, DDNNE ET AL 2,170,515

SENS ITOMETER Filed Feb. 8, 1936 RECORDER #2 EE'COEOER #1 AMPL lF/EE #2 I r25 I i I v I 2 I 36 #1 Patented Au 22,1939

sausrromn'rnn .Iohn C. Dionne, Somerville, Mass, and l ienry W. Kcevil, Highland Park, Ill.

- Application February a, 1936, Serial No, 62,935 6 Claims. (m.- 115-183) This invention relates to a device for quickly checking the sensitivity of an amplifier, relay or other electrical apparatus. I

Further and other objects and advantages will become apparent as the disclosure proceeds and the description is read in conjunction with the accompanying drawing, in which:

Fig. 1 is a, perspective view of a sensitometer made in ccordance with this invention; and 10 Fig. 2 a diagrammatic view of the electrical circuit and parts associated therewith.

For the purpose of complying with section 4888 of the revised statutes, 8. preferred embodiment of the invention has'been chosen for illustration and description, butit will be understood that the appended claims are not ,limited by the details of the embodiment shown and described unless required by the prior art.

There are many cases in which it is desirable to quickly check the sensitivity of a particular piece of'electrical apparatus, such as a relay, an, amplifier, etc. This is particularly true in setecting flaws in railroad track because as the conditions of.the track change, it is necessary to make corresponding changes in the sensitivity of the'detecting apparatus. The use of the sensitometer in conjunction with flaw detecting apparatus is shown diagrammatically in Fig. 2, and for convenience in explaining the electrical circuit of the sensitometer,

it will be described with particular reference to this use. 4

Referring now to Fig. 2, the reference characters II and I l referto the'rails of a track, each rail being suitably energized by a direct current generator I! adapted to pass at low voltage, high amperage current throughv the rail.

The passage of the current through therails sets .up an electromagnetic field'surrounding them 40 and pickup units comprising oppositely connectedv detector coils l3, are adapted to move over the surface of the rails and detectvariationsiri the magnetic flux caused by flaws or other defects in the rail. When the .pickup unit traverses a '45 field of greater or lesser intensity than thenormal held, a current is induced'in the coils, which is suitably amplified and recorded-.-

Since the method of fia'w detection constitutes no :part of thisinvention and is used merely to' goshow environment in which the sensitometer may advantageously be used, further description is deemed unnecessary. I

As a matter of convenience, the pickup unit,

, amplifier and recorder associated with the rail I be referred to as pickup No. 1. amplifier between the points 20 and 2|.

No. 1 and recorder No. 1 and the corresponding units associatedwlth the rail II will be referred to as pickup No. 2, amplifier No. 2 and recorder No. 2. r The electrical circuit for the sensitometer in- 5 cludes a source it of electro-motive force (which may be a 1.5 volt, dry-cell battery), a milliam- -meter l5 (preferably Weston Model 301 milliam- -meter reading from 0 to 1 milliampere, a product of Weston'Electrical Instrument Co., New- 10 ark, N. J.), a snap switch l6 (preferably a toggle switch of the type used in radio work, as, for example, Arrow H- -H toggle switch, catalogue No. 6060, a product of Arrow-Hart-Hegiman Electric 00., 701W. Jackson Blvd, Chicago, 15

is closed gives a particular wave form repre- 2s senting the change in'the potential difference The purpose of v the sensitometer is'to produce a known voltage U change across the resistance l9 and then apply it to theelectrical apparatus whose sensitivity 30- is to bechecked.

Since the wave format the output of the am-, plifier produced by the pickups when traversing the electro-magnetic field in the region of a flaw is substantially a sine curve, it is desirable to 35 have the voltage wave producedby the 561151130111- eter of approximately the same form when it leaves theamplifier. Since the electrical circuit which has thus far been described, sets up a voltage wave, the length of which is somewhat shorter. 40 than that produced by the pickups, a condenser '22 is connected across the resistance I! to lengthenthe wave and produce a wave form which more nearly approximates that produced by the pickup coil (preferably the condenser '22 has'a capacity of twomicrofa'rads-ln A double-pole,'double-throwswitch- 23 enables {the sensitometer to be connected selectively to either amplifier and other double-pole, doublethrow. switches 24 and 2! enable the amplifiers to be selectively-connected either to the pickup units or. to ,the sensitometer. Obviously, when the switch handles; generally designated 20 of the switches 24 and 25, are moved outwardly, the am-' pliflers-are connected to the pickups and when the handles are thrown inwardly, the amplifiers are disconnected from the pickup units and may be selectively placed in circuit with the sensitometer by proper manipulation of the switch 23.

it is not essential that the switches 2t and 25 he provided because the amplifiers may be tested by connecting the sensitometer in parallel with the pickups but the, results are not quite as accupress high frequency surges of current through binding posts v36 topickup No. 2.

the circuit at the instant when the switch Ii is opened or closed.

'rn sensitometer is housed within a cabinet or casing having a window 3| in its front face through which the milliammeter I5 is exposed. The variable rheostat I8 is. preferably mounted 'within the cabinet so that the control knob -32 is beneath the ammeter IS. The switches Ii, 23, 2|

and 25 are conveniently located on the front face of the cabinet as shown in Fig. 1.

A- plurality of binding posts are provided on the. top wall of the casing for connecting the sensitometerv to. the amplifiers and pickups, the binding posts being adapted. to be connected to pickup 0. 1, binding posts 34' to amplifier No. 1, binding posts 35 to amplifier No. 2 and In using the sensitometer, each amplifier is first adjusted (by means of the grid bias or any other conventional manner) so that it is sensitive enough to pick up and enable the'recording apparatus to record fissures of known size. The

sensitometer is then calibrated to that setting of the amplifier by adjusting the rheostat it until the closing of the switch IE will just harely'cause the recorder to operate. A standard is thereby established for setting the amplifier to greater or less sensitivity.

Q To make a test of amplifier No. 1, the switches are thrown to the position shown in Fig. 1, that is, with the switch 24 to the left and the switch 23 to the right so that the sensitometer is connected to "on? position and the current through the circuit is adjusted by moving the control knob of the rheostat I8 until the current through the circuit, as indicated by the needle 31 of the ammeter, is of some known predetermined strength, (represent ed by the figure 10, for example, on the meter scale). The switch I is then turned oifand im-.

mediately turned onagain. If this'operaflon causes the recorder to operate, the sensitivity of the amplifier is reduced by suitable adjustment and the test is repeated until the manipulation of the switch li'just barely causes the recorder to operate. The amplifier is then at the proper setting for sensitivity to input wave represented by the,arbitrary figure '10.

any other value, a similar procedure is followed. .While it is preferable to use the making of the electrical. circuit in testing for sensitivity, it will be understood that the opening of the electrical circuit. by the switch It bears a functional rela-' tionship to the system which enables it'to be used V the a b fler.

as a criterion if desired. 7 we claim as our invention: Y 1. In a sensitometer, a casing, an electric meter The switch 16 is thenmoved to.

in'the casing having an exposed. meter face,

electrical circuit associatedwith the meter indiiference is adapted to be established upon.

manipulation ofthe switch, said resistance being adapted to be connected to an electrical device whose sensitivity is to be tested, and a condenser connected across the resistance. I

2. ma sensitometer, a casing, an electrlc meter in the casing having an exposed meter face, an

electrical circuit associated with the meter including a source of electromotive force, a switch and aresistance across which a given potential difference is adapted to be established upon.

3. A sensitometer for use with ilanig detecting,

apparatus including. an induction coil and an amplifier associated with the coil, said sensitometer comprising a casin an electric meter in the casing having an exposed meter liace, an

electrical circuit, associated with the, meter including a source of electro-motive .force, a switch and resistance across which a given potential (111- y ference is adapted to be established upon manipulation of the switch, and a condenser, connected across the resistance and havinga capacity which produces a voltage wave-form across the resistance which corresponds substantially with the voltage wave-form across the induction coil of the flaw detecting apparatus whenever a flaw is encountered.

4. For use in a device of the class described, an electrical circuit comprising a source of. electromotive force connected to a resistance, a switch for disconnecting the electro-motive force from i the resistance, means for. connecting theresistance,to electrical apparatus, the,,,.sensitiv ltyof which is to be tested, and a condenser connected across the resistance. I

5. In a sensitometer, acasing, an electric meter in the casing havingan-exposedmeter face, an.

opening the circuit, means for controlling the" flow of current through the circuit, a across which a given potential is adapted to be-establishedupon manipulation of the switch, means for controlling the iormof the To set'the amplifier for a sensitivityof 20 or.;' mmmmuim connecting the ihput oi the amplifier to opposite sides of the resistance whereby manipulation or JOHN c.- moans.-

mam! w. mm. 

